Age-Related Brain Structure Differences, by Age of Onset, in Older Adults with Bipolar Disorder

Abstract

<h3>Introduction</h3> While brain structure during adolescence and early adulthood has been relatively well characterized in bipolar disorder (BD), it is still unclear how the brain's structure is affected by the illness in later life, and whether age of onset may influence age-related changes. <h3>Methods</h3> High resolution structural magnetic resonance images were acquired at 3 Tesla in 103 individuals with BD and 98 healthy controls (HC), ages 40 to 79 years. Categorical group comparisons (BD vs. HC), and analyses for group differences in age-related patterns, were performed for cortical thickness and grey matter volume. The BD group was also subdivided by age of first mood symptom onset, being either age 25 years and over (adult-onset, <i>n</i>=21) or below age 25 years (adolescent-onset, <i>n</i>=82), and the BD subgroups were compared to controls in a three-way analysis. <h3>Results</h3> Compared to the HC group, the overall BD group was characterized by lower cortical thickness within the insula and parahippocampus regions (<i>pcorrected</i>= 0.0054), and lower grey matter volume within the hippocampus, thalamus and putamen (<i>pcorrected</i> = 0.001). Significant age-related differences were not detected between the overall BD group and HC group. However, when individuals with BD were divided by those with adolescent or adult onset of the illness, the adult-onset BD subgroup showed significant age-related declines in insula and parahippocampal thickness, and hippocampal, thalamic and striatal grey matter volume, compared to the early-onset BD subgroup and HC group (<i>p</i> = 0.021). <h3>Conclusions</h3> The findings support structural abnormalities within the insula, parahippocampus, hippocampus, thalamus and striatum in adults with BD ages 40-79 years. Age-related decreases within the insula, parahippocampus and hippocampus may occur particularly in individuals with BD with onset after the age of 25 years. The results suggest that individuals with later onset of BD may be at a greater risk for age-related abnormalities in brain structure in brain systems that subserve emotional and cognitive processes. <h3>Funding</h3> Funding for the project was awarded by the National Institute of Mental Health.